Force on two cables holding a liquid-filled container against a wall

In summary: This means that the net force must pass through O.In summary, the conversation discusses the calculation of weight force and force due to water pressure on a curved plate. The resulting force between the two forces is calculated and must pass through point O. The conversation also mentions the need to balance two torques around the hinge C and the assumption of weight force being applied at the center of mass of the water. It is also mentioned that the net force of the water on the plate must pass through O due to the zero moment of the force.
  • #1
A13235378
50
10
Homework Statement
A plate is in the shape of a quarter cylinder of radius R and length L. This plate is hinged at C to a vertical wall and can rotate freely about C. The end A of the plate is tied to the wall using two horizontal cables the other cables is parallel to OA and the two cables are placed symmetrically). the space between the wall and the plate is filled completely with water (density=rho) Neglect the weight of the plate and calculate the tension in each cable .
Relevant Equations
p = rho . g . h (pression)
Before, sorry for my English, it is not my native language

I already have the solution to the issue, I just didn't understand a step.

1) Calculation of weight force (vertical):

$$ F_v = \frac{\rho \pi R^2 . L .g}{4}$$

2) Calculation of force due to water pressure on the plate (horizontal)

Mean pressure . effective area = $$ \frac{\rho . g . R}{2} . RL = \frac {\rho g R^2 .g} {2} $$

From this, the resulting force between the two forces is calculated and its direction must pass through point O.

Sem título.png

My doubt is exactly this: why do you need to go through the O point?
 
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  • #2
A13235378 said:
From this, the resulting force between the two forces is calculated and its direction must pass through point O.
Four forces act in this diagram: the tension of the two cables, the weight of the water and the force through the hinge C. I don't know which two forces you refer to here. Nor do I understand what you mean by "need to go through the O point".

I would find it simplest to approach this problem as a need to balance two torques around the hinge C. One torque is provided by the weight of the water. Find the location of the centre of mass of the water and assume the weight force is applied there in order to calculate a torque around C. Then calculate the torque around C provided by the cables in terms of the tension T in each cable.
 
  • #3
A13235378 said:
Why do you need to go through the O point?
Consider a small patch of the curved plate. The water pressure exerts on it a force normal to the plate. This force has zero moment about O, so the net force of the water on the whole plate has no moment about O.
 

What is the force exerted by the liquid on the container?

The force exerted by the liquid on the container is equal to the weight of the liquid. This is known as the hydrostatic force and is calculated by multiplying the density of the liquid by the volume of the liquid and the acceleration due to gravity.

How does the angle of the cables affect the force on the container?

The angle of the cables can affect the force on the container by changing the direction of the force. The force exerted by the cables is split into two components - one perpendicular to the wall and one parallel to the wall. As the angle of the cables increases, the perpendicular component decreases and the parallel component increases.

What is the relationship between the weight of the container and the force on the cables?

The weight of the container has a direct relationship with the force on the cables. As the weight of the container increases, the force on the cables also increases. This is because the weight of the container is being supported by the cables.

How does the depth of the liquid in the container affect the force on the cables?

The depth of the liquid in the container can affect the force on the cables by changing the hydrostatic pressure. As the depth of the liquid increases, so does the hydrostatic pressure, which in turn increases the force on the container and the cables.

What other factors can affect the force on the cables holding a liquid-filled container against a wall?

Other factors that can affect the force on the cables include the density of the liquid, the acceleration due to gravity, and the material and strength of the cables. Additionally, any external forces acting on the container or the wall can also impact the force on the cables.

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